Apparatus for treating aluminous materials



Feb. 7, 1928.

E. MOLDENKE APPARATUS FOR TREATING ALUMINOUS MATERIALS Original FiledSept. 28. 1 20 Patented Feb. 7, 1928 UNITED STATES 1,658,457 PATENT,OFFICE.

EDEL MOLDENKE, F HARRISONBURG, VIRGINIA, ASSIGNOR TO MOLDENKE PROCESSCORPORATION, OF WATCHUNG, NEW JERSEY.

APPARATUS FOR TREATING ALUMIN OUS MATERIALS.

Original application filed September 28, 1920, Serial No. 413,402.Divided and this application fled April 27, 1923.

This application is a division of applica t1on Serial No. 413,402, filedSeptember 28, 1920, Patent N 0. 1,457 ,7 87.

The invention relates to processes of 'treat- I 5 ing aluminousmaterials; and. it comprises a process of treating hard-baking or hardsetting materials, more particularly applicable in methods of roastingaluminous materials with sulfuric acid, wherein such hard H) baking orsetting material is heated in contact with or on a flexible surfaceduring the hardening period, being thereafter stripped therefrom bycurving such surface, said material being in a layer sufliciently thickto us have, after the hardening and at the time of stripping, enoughmechanical strength to peel off in fragments at the time of curvature;asin a method wherein a layer ofa pasty mixture of sulfuric acid andaluminous material (such as bauxite, clay, alunite, etc.) is slowlyconveyed through a heated chamber during the period in which a tendencyto stick and cake develops, conveyance being on a belt of strong andsmooth material, such as sheet steel oriron and the layer being ofsubstantial thickness, the layer broken off by curving the belt, the framentary hard material comminuted and nally roasted in the usual ways;all as more fully hereinafter set forth and as claimed.

In various methods of treating various chemical materials and mixturesby heat in metal pans or vessels, there is a development of stickinessand hardness during the first 5 stages of heating; the: materials tendto bake on the pan. Usually this tendency is resistedby the use ofpowerful stirring or cutting devices which kee the mass comminuted. Itis however often difiicult to 0 find structural materials resistant tochemical actions at high temperatures and of sufficient strength toexert the power required; and in any event, it is usually'impossible tokeep all the surfaces of the pan clean and free from baked-onaccumulations. In'many cases, this necessitates frequent stoppage andcooling to permit cleanin These dilficulties are particularlynoticeable'in methods of roasting various aluminous materials (clay,bauxite, alunite, etc.) with sulfuric acid, in regard to which]: shallmore particularly describe-the present invention. It is howeverapplicable in many other cases, as infdehydrating such salts ascrystallized sodium sul- Serial N0. 635,151.

fate, alum, etc., which first melt in their Water of crystallization andthen bake hard.

In the present invention, I segregate the heating operation intodifferent stages and .perform the first, or that during which bakmg onoccurs, on a thin smooth flexible mem-' her; the material being heatedas a layerof substantial thickness. In most cases I use thin metal. Thelayer should be thick enough so that when hardening is effected, thelayer should have substantial inherent strength of its own so that oncurving the metal member the layer does not merely crack and follow thecurvature but breaks oif or peels away in fragments. Having so heatedthe material, the holder is curved, the fragments collected and(usually) comminuted and the heating completed in appropriate apparatus.In the second or final heating agitation is often not necessary and inany event does not require the usual 0werful agitating and means.

As stated, I shall more particularly describe the present invention inrelation to the treatment of aluminous materials with sulfuric acid, butwithout limiting its application thereto. In various current methods oftreatin clay, bauxite or alunite with sulfuric aci the finely .mixed'with sulfuric acid and the mixture heated or roasted in a pan or drumrovided with powerful agitating means. he mixture is at first a'sort ofpaste or mud, like any other intimate mixture of a fine-grainedsolid anda'liquid, but as chemical'reactions go onit becomes sticky and stiff andfinally hard, forming a dry caked mass which is again comminuted by theagitating means to give a dry granulated body of material. Much power isrequired and high temperatures are cften"attained.-300 to 400 C.

and higher. With the apparatus ordinarily used, much trouble isexperienced in the mixture sticking to the pan and baking on; and it isusually necessary in these. operations to stop periodically and cleanup, thereby losing time and labor. Baked-on cutting or brea 'ng groundmaterial is accumulations frequently are so hard as to require removalwithhammer and chisel.

In the present invention I first heat the initial mixture until it haspassed through the pasty and sticky stages and becomes hard and caked,this heating being performed on a flexible or bendable member of somekind. This member is best a sheet iron or steel belt traveling through ahot chamber and passing over rolls or pulleys of relatively largediameter. I then comminute the caked mass dropping or peeling off thebelt and finish by heating elsewhere. A layer of the paste of acid andsolid material is carried through a chamber which may be internally orexternally heated as may be convenient. The final temperature of thematerial passing through it is made as high as may be necessary toproduce a hard and caked mass without substantial loss of sulfuric acidby volatilization; A layer of the paste fed on such a belt travelingslowly through such a hot chamber of such a length and such atemperature as to dry and cake the mass at a point just prior to theexit of the belt from the heating chamber if of suflicient thicknesswill be automatically stripped off and fall from the belt as the beltchanges its curvature in going around the pulleys or rollers. Ifthinner, the layer may simply crack and follow the belt, from which itis then hard to detach it. As noted, these masses are sometimes so hardand adhere so tightly to iron and steel as require hammer and chisel fordetachment, coming off chip by chip. How ever, with a smooth-surfacedmetal belt and a sufliciently hard and strong layer, the hardness andstrength themselves cause stripping in the described way, and the cakedmass tumbles ofi' in a hard fragmentary condition. It may then be easilyground and comminuted. As grinding need not be at any high temperature,any convenient usual type of breaking or grindlng' machinery, such asrolls, may be used. The dry or semi-dry granular material so producedmay then be finished in the usual pans or drums.

The present process is particularl useful in connection with the processof ltichard Moldenke of utilizing alunite, Patent No. 1,282,273, October22, 1918. In this rocess finely comminuted alunite is heate in a closedvessel with concentrated sulfuric acid in suflicient amount to form amass which is initially pasty. Digestion is at a temperature suflicientto cause a free evolution of fumes; these fumes however not beingpermitted to escape. After this operation the valuables of the materialbecome soluble in waterand can be recovered. In utilizing the" resentinvention with such a process as t at of said Richard Moldenke, insteadof directly delivering the pasty mixture of acid and alunite into thetreatment vessel or roaster, this mixture is first assed through aheated chamber on a flexib e conveyer, such as a belt, until it isconverted into a hard, caked and non-sticky form, is flaked off asdescribed and is then comminuted, and the comminuted material heated andfurther treated in the mannervertical section, certain parts being shownin elevation, element A is a mixer consisting of a casing 1, havingrevoluble breaking arms 2 therein actuated by shaft 3. Pulverizedalunite, clay or bauxite is supplied to this device by hopper 4, whileacid is added at 5. The aluminous material and the acid are mixed to apaste in this device. The paste isdischarged through gated outlet 6 iutoa feeding device 7. This feeding device is positioned immediately abovea belt or the like 8 which, for the present purposes, may be made oflight sheet iron and feeds a layer of the pasty mixture thereon, thethickness being adjusted by gate 9. As shown, the conveyor passes overtwo pulleys or wheels 10 and 11 and through a roasting or drying chamberB. This chamber is provided with roof 12, floor 13, and receives hotproducts of combustion or other heating medium through a number of ports14 above and below the part of the conveyor going through the chamber.Waste gases are discharged through ports 15 and reach dampered chimneyor stack 16. The return of the belt as shown is underneath the floor ofthe roasting chamber. The depth of the layer, the length of the chamberand the speed of passage of the belt are so adjusted that the pastymixture supplied on the belt is hard and caked by thetime it reaches theend of the chamber.. The temperature of the chamber is carried as highas is practical without'loss of sulfuric acid. The hard, caked materialon the belt is torn from it and breaks off as the belt changes'curvaturein going around the pulley 11. The caked material 17 passes down a slide18 into diagrammatically shown grinding device 19, where it is brokenand comminuted. The end of the slide 18 may serve as a doctor to cleanthe belt of any adhering loose material. From the grinding means thematerial goes into hopper 20 on an ap aratus.

C of the general type of that shown y said Richard Moldenke, Patent No.1,282,273.

If not enough acid has been added in the first place, or if conditionsin the drying chamber have been improper with resultant loss of acid byvolatilization and escape, more acid ma be here added at 21. Such anaddition 0 acid is not usually desirable, since it may lead tothematerial sticking and caking again, but this secondary caking is notusually serious. The comminuted material is agitated within this deviceby arms 22 kept in rotation by pulley 23/ Heat is iminc , which maycontain a little sulfuric acid as a collecting means. Roasted materialis delivered by chute 27 into tank 28. As shown, this is adapted to thetreatment of roasted alunite and is provided with steam pipe 29 forleading in open steam to agitate the mixture of roasted material andwater.

A sheet iron belt passing over pulleys or rollers of large diameter isthe most convenient form of apparatus for the present purposes, but ofcourse any other flexible mem-.

ber with means for changing its curvature may be used, such as a drumwith a flexible surface. The main point is to make a cake of-sufiicientthickness, hardness and strength to resist deformation or minutedisintegration and then peel it off by deforming the carrying surface.In so deforming the carrying surface, compression, tension and shearingstrains are set u in the cake bythe adhesion of cake and surface. Forthe present purposes, it is necessary to have sufficient thickness ofthe cake to give it strength to resist, for the most part, these variousstresses tending to its disintegration so that when the carrier curvesit will not do so but will tend to continue on it the original path.

The apparatus shown and described may be used for many other purposesthan hottreating alunite with sulfuric acid; it being also useful forthe like purpose of hot-treating clay or bauxite in the manufacture ofsulfate of alumia (aluminum sulfate); for the dehydration of sodiumsulfate, alum, etc. Sodium sulfate when heated melts in its water ofcrystallization and then becomes a hard frothy mass which is difficultto dry completely in any technical apparatus. If fed on the belt andheated in the manner shown, it is converted into a cake which may becomminuted and then dried in any apparatus, such as that shown at C.'Such a flexible abruptly curved member may also be used in otherrelations where heating is not involved but cakes are formed, as forinstance, in making ice, a layer of ice being first made and then peeledofi in fragments.

Having thus fully described the invention, what I claim as new anddesire to secure by Letters Patent is:

1. Apparatus of the character described embodying a flexible carrier,means for mixing finely divided aluminous material and sulphuric acidand adapted for depositing the resulting paste in the form of a layer onthe carrier, means adapted for heating said layer, while on the carrier,to cake the paste, means for flexing the carrier to free the caketherefrom, grinding mechanism adapted to receive the cake dischargedfrom the carrier and to comminute it, and means adapted to heat the thuscomminuted cake.

2. Apparatus of the character described embodying an endless flexiblebelt mounted to travel, a hopper positioned to deposit finely dividedaluminous material and an acid in the form of a paste upon the belt,

means for heating the paste while on the belt toefiect caking thereof,and rollers about which the belt is mounted to travel, whereby the cakedsubstance is caused to break and the other roller, means adapted to heatthe material at a suflicient temperature to cake it before it reachesthe latter roller, whereby the cake will be sufiiciently hard to befreed from the belt as it passes over said latter roller, grindingmechanism for receivin the cake thus discharged from the belt an forinding, and roasting mechanism for receiving the ground material fromthe grinding mechanism and adapted for heating it to I a sufiicienttemperature.

In testimony whereof, I have signed the foregoing specification.

EDEL- MOLDENKE.

